A short brass rod has 6 differently coloured spots, in the same order on each side. A spectator chooses a number, a quick shake of the rod and they all change to the colour at that number. They'll want to see the trick again, so a quick shake and they all go back to different colours. The magician now chooses a number and counts to that colour, this time the spots change to the new colour (both sides). The rod is immediately handed out for examination.